Method and apparatus for inhibiting roll pickup in continuous annealing of steel strip



Patented Sept. 1, 1953 METHOD AND APPARATUS FOR, INHIBITIN G ROLL PICKUP IN CONTINUOUS ANNEAL- ING OF STEEL STRIP Harry F. Shannon, Pittsburgh, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Application May 18, 1950, Serial No. 162.669

6 Clains. (CI. 148-215) This invention relates to provislons for inhibiting roll pick-up" in the continuous heat-treatment of flat-rolled metal products.

The processing of certain classes of fiat-rolled metal products, e. g., steel strip, and particularly silicon-steel strip from which electrical sheets are sheared, preferably includes annealing or normalizing, usually in a decarburizing atmosphere. This treatment is customarily effected by the use of a continuous furnace having driven rolls for supporting the product and conveying it therethrough. The rolls which may be of ordinary steel or a heat-resistant alloy, show a strong tendency to pick up particles of combined silicon and iron oxide within a relatively short time. The oxides of iron and silicon, separately, have high melting points but when combined in the proper amounts they form the compound known as fayalite which has a relatively low melting point. This compound forms on the surfaces of silicon-steel strip during continuous annealing at elevated temperatures in an oxidizing atmosphere. Particles of the fayalite thus formed are tacky at the Operating temperature of the furnace and adhere to the surface of the metal conveyor rolls, thereby forming so-called pick-up spots. The particles build up in localized areas forming projections on the rolls which mark the strip in a manner designated as "dimpling." This renders the material unusable for most purposes. As a result, it frequently becomes necessary to shut down the furnace and clean off the rolls with the attendant increase in maintenance cost and loss of production.

I have invented a novel method for inhibiting oxide pick-up by the rolls of a continuous furnace and apparatus for carrying out such method easily, Conveniently and effectively. My method contemplates the maintenance on the conveyor rolls of a film of a material which is not wet by the iron and silicon oxides on the strip, thus preventing their adherence to the metal of the rolls. The material used to form a film on the surface of the rolls may be graphite or other refractory material such as metallic oxides. The apparatus of my invention includes means for supporting a mass of the lm-forming material in contact with the rolls traversed by the product, so as to have wiping engagement with the roll surfaces.

A complete understanding of the invention may be obtained from the following detailed description and explanation thereof which refer to the accompanying drawlngs illustrating a preferred embodiment and a modification. In the drawings,

Figure 1 is a central vertical section, largely diagrammatic, taken longitudinally through a continuous strip-anneaiing furnace having the invention incorporated therein;

Figure '2 is a partial horizontal section taken along the plane of line II-JI of Figure l, showing :parts in plan;

Figure 3 is a view partly in elevation and partly in section, taken along the plane of line III-III of Figure l; and

Figura 4 is a transverse section through one of the conveyor rolls taken along the plane of line IV-IV of Figure 3.

Referringin detail to the drawings and, for the present, to Figure 1, a strip-annealing furnace indicated generally at u comprises a refractory-lined enclosure laid up within a conventional binding abricated from steel plate and rolled sections (not shown) in the known manner. The urnace has an entrance opening I i at one end and an exit opening !2 at the other adapted to permit the passage of strip therethrough from an uncoiler at the entrance end to a recoiler at the exit end. The furnace may' be heated by any suitable means, i. e., electric; resistors, radiant combustion tubes or the like.. A controlled atmosphere, usually decarburizing,. is supplied to the furnace chamber by any convenient means (not shown).

In order to maintain each point along the strip at the temperature necessary to producedecarburization, for the required length of time, the strip is trained alternately over conveyor rolls it in an upper series designated |3 and a lower series designated l3 The rolls !3 have shafts i l extending through the side walls of the urnace and journaled in any suitable bearings carred thereby. The shafts are driven in the known manner by any convenient mechanism. The arrangement of the rolls in the two series as shown is such that the strip, when properly trained thereover is caused to make a plurality of passes upwardly and downwardly throughout substantially the full height of the chamber. The cylindrical bodies of the rolls may be fabricated from steel plate. Instead of a unitary oylinder, the roll bodies may consist of a plurality of discs spaced along the shaft.

Bafiies !5 and !6 clivide the interior of the furnaoe chamber into several chutes traversed successively by the strip in its alternat upward and downward passes. A cradle l'l of steel bars, preferably heat-resistant steel, is positioned above each lower roll l3 the ends of the bars being embedded in the bafes and furnace walls. A block of graphite !8 is loosely confined in each cradle and rides on the roll therebelow. On rotation of the roll, -itwipes the block and thereby acquires a film of 'graphite on itssurface. This film is not Wet by the oxides on the surface of the strip traveling around the roll and the latter therefore does not pick up such oxides. As a result, the roll surface remains clean and smooth over a long period of operation and the' strip is consequently not marked by its contact there- With. short pieces of bardh weldedtovthe Cradle prevent tilting of the blc'cks !8.

The upper rolls [3 have tables [9 therebelow on which graphite blocks [8 areloosely confined as by an edge flange or the like. Each table is carred on a tilting frame 20 pvoted=at-2l to the side walls of the furnace. A counter-weight Suspended from the outer .end ofeach rame constantly urges the blocks 18 on tables 9 .into

-Wipng engagement `with rolls 13 .for the purpose of appiying a graphite'film thereto. The

table' and "frame are preferably v of heat-resistant to give them the block form illustrated. v Another 'material which maybe used is-molybdenum clisulphide. It is generally similar tographite in its eiiect for thepurpose of this invention.

Experienceshows that the invention permits the operation of a' continuous .strip-annealing -urnace for much longer periods than otherwise possible, without the occurrence of roll pick-up toan objectionable degree. The invention thus materially -reduces 'the maintenance cost of the furnace and increases its production.

Iclaim: 1. In a method of treatngsilicon-steel strip,

groupconsistingof magnesia, alumina and silica.

*4.'lthecombinat`on with a strip-annealing furnace' having horizontal metal conveyor rolls ex- `tending.ther'eacross'.:;of a pair of bars mounted onthe'interioroi .the furnace walls adjacent each roll and a mass f refractory material carried by..sad-bars.-n.contact with said roll, continuo`us1y applyingthereto a film inhibiting the pickup ofoxides from the strip.

5. The combination defined by claim 4 characterized by u saidbars; -forming a cradleabove the roll adapted tcconfine said mass.

6. The combinationdefined by claim 4 characterized by atablebelow the roll supported on :table upwardly. -.toward the roll, said means being -carried on said bars.

said'bars and-counterbalancing means urging the HARRY- F. SHANNON.

References Cited in the file of this patent i UNITED, STATES PATENTS 'Number Name Date 6691165 'Reichhelm Mar. 12, 1901 l,-6-26;585 Marden et al May 3,1927 13765955 Von Maltitz et al. June 24, 1930 '1,956j401 -Russ Apr. 24, 1934 -2,07,518 *Fraser'et al. Oct. 13, 1936 21353347 Hazelett Oct. 27, 1936 1248113010 CoXe Dec. 12, 1939 2,199,191 =Tour Apr. 30, 1940 2345181 Cooper et al. Mar 28, 1944 v 23128344 Stookey Sept. 30, 1947 i 2534973 Ipsen et al. Dec. 19, 1950 i 2593578 v Ornitz July 15, 1952 

4. THE COMBINATION WITH A STRIP-ANNEALING FURNACE HAVING HORIZONTAL METAL CONVEYOR ROLLS EXTENDING THEREACROSS, OF A PAIR OF BARS MOUNTED ON THE INTERIOR OF THE FURNACE WALLS ADJACENT EACH ROLL AND A MASS OF REFRACTORY MATERIAL CARRIED BY SAID BARS IN CONTACT WITH SAID ROLL, CONTINUOUSLY APPLYING THERETO A FILM INHIBITING THE PICKUP OF OXIDES FROM THE STRIP. 